The Cataract Panel of the NEI Advisory Council in its 1982 five-year plan has recommended that two of its program development priorities be "to find means of preventing or slowing cataract development" and" determine through epidemiologic studies factors that increase the risk of developing cataract". The goal of the proposed study is to obtain such information as part of the ongoing Physicians' Health Study (PHS), a randomized, double-blind, placebo-controlled clinical trial of aspirin use (325 mg on alternate days) in reducing cardiovascular mortality and beta-carotene in reducing cancer incidence among 22,071 male U.S. physicians aged 40 to 84 years. The proposed study will utilize the PHS database to assess the effect of low-dose aspirin on cataract development. Thus, it will be possible to provide a valid test of the aspirin-cataract hypothesis without the expense of funding a large clinical trial. Baseline information was collected on the participants in 1982, and annual follow-up questionnaires request information on diagnoses of cataract. Baseline blood samples were collected on two-thirds of those randomized. All reported diagnoses of cataract will be confirmed by medical record review. Baseline blood samples for cases and controls will be analyzed for selenium and vitamin E levels. It is expected that by the end of the follow-up period (June, 1990), there will be approximately 960 incident cases of cataract. The primary analysis will be incidence of cataract in the aspirin and placebo groups. In addition, Cox proportional hazards models will be used to determine whether there is a difference in time to cataract diagnosis. Factors which have been suggested to be cataractogenic also will be investigated using nested case-control methods, matching on control (for age and time of randomization) to each cataract case. Prospective data on these factors include age, blood pressure, blood cholesterol, height, diabetes, medication use, and history of previous eye trauma or surgery. In addition, the possible associations between history of vitamin E intake, baseline plasma concentrations of vitamin E and selenium and cataract will be explored.